Differential gas system for gasoperated firearms



Jan. 26, 1965 A. J. LIZZA 3,166,983

DIFFERENTIAL GAS SYSTEM FOR GAS-OPERATED FIREARMS Filed Sept. 18, 1963 Figi l INVENTOR. AIL her .1 Lizz 11 WMX 3,166,?83 DEFERENTIAL GAS SYSTEM FOR GAS- GPERATED FIREARMS Albert J. Lizza, North Wilbraham, Mass, assignor to the United States of America as represented by the Secretary of the Army Filed Sept. 18, 1963, Ser. No. 39,902 v 3 Ciaims. Cl. 89l91) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to gas-operated automatic fire arms and is more particularly directed to an improved piston and cylinder arrangement for imparting recoil movement to an operating rod.

In gas-operated =firearms wherein the discharge gases are taken from the barrel and accumulated in a gas cylinder for driving a piston to energize a recoiling member, such as an operating rod, considerable stress and shock is normally imparted to the operating rod and the recoiling parts associated therewith by the relatively high initial velocity of the piston. These high stresses are responsible for excessive wear of the recoiling parts and frequently result in premature breakage thereof especially in sustained automatic fire. Although attempts have been made to utilize spring means for cushioning the initial velocity of the gas piston, these efforts have generally been unsuccessful primarily because springs are not capable of transmitting identical forces during each successive cycle of firearm operation.

Accordingly, it is a general object of this invention to provide a gas cylinder and piston arrangement for automatic firearms which will increase the endurance life of the recoiling parts by minimizing the shocks and stresses imparted thereto by the initial velocity of the piston during each cycle of operation.

It is a further object of the present invention to provide an improved gas cylinder structure for automatic firearms which can be positioned almost completely forward of the gas port in the barrel in order to provide an operating rod of maximum length.

Another object of this invention is to provide a gas piston in an automatic firearm which can be readily tailored to furnish optimum power characteristics even in firearms intended for use under special environmental conditions, such as those encountered in Arctic regions.

Still another object of this invention is to provide an improved gas cylinder structure for an automatic fire arm wherein the initial velocity of the gas piston therein can be precisely controlled to permit the utilization of smaller and lighter recoiling parts.

It is a particular object of this invention to provide an improved gas cylinder assembly for an automatic firearm wherein the gas piston is specifically constructed so that recoil movement thereof will not be initiated until the force imparted thereto by the entry of the discharge gases into the cylinder is overcome by the opposing force of the gases which accumulate in front of the driving face on the piston.

The present invention essentially comprises a gas piston having an enlarged forward head portion in slidable engagement with the interior walls of a gas cylinder secured to the exterior of the barrel. The cylinder is provided with a gas port adjacent the rear end thereof and in axial alignment with a corresponding gas port in the barrel. A plurality of longitudinal gas passages are circumferentially spaced about the head portion of the gas piston to admit discharge gases into an annular area surrounding United States Patent 3,166,983 Patented Jan. 26, 1965 a stud of reduced diameter which projects rearwardly from a plug fixed in the front end of the gas cylinder. During the entry of the discharge gases into the gas cylinder, pressure is exerted against the surface areas disposed between the spaced gas passages in the head portion of the gas piston to retain such piston in a stationary position. However, this delay in the initial recoil movement of the gas piston is terminated as soon as the force of the discharge gases which accumulate in the annular area adjacent the front end of the piston exceeds the force imparted thereto by the incoming gases.

Other objects and advantages of the invention will be apparent from the following specification and the accompanying drawings which are for the purpose of illustration only and in which:

FIG. 1 is a fragmentary longitudinal section of a gas operated firearm showing the position of the gas piston as the fired projectile is approaching the gas port in the barrel;

FIG. 2 is a sectional view similar to that of FIG. 1 but showing the position of the gas piston after the initial recoil movement thereof following the passage of the fired projectile beyond the gas port in the barrel;

FIG. 3 is a cross-sectional View taken along line 3-3 in FIG. 2 to show the relationship between the gas piston and the surrounding cylinder; and

FIG. 4 is a perspective view of the gas piston.

As illustrated in the drawings, the firearm in which the present invention is incorporated is provided with a barrel 12 extending forwardly from a conventional handguard 14. An operating rod 16 biased forwardly by a spring 17 is slidably mounted below and parallel to barrel 12 for passage through handguard 14 and is utilized to unlock the breech by means of suitable linkage (not shown). The exterior diameter of barrel 12 is slightly enlarged, as shown at 18 and 20, to respectively seat a pair of longitudinally spaced mounting rings 22 and 24 projecting upwardly from a gas cylinder 26. Barrel 12 is provided with a conventional transverse gas port 28 located in enlarged diameter portion 18.

Gas cylinder 26 is also provided with a transverse gas port 30 adjacent the rear end thereof in position for axial alignment with gas port 28 when gas cylinder 26 is assembled onto barrel 12 in abutment with a cap 32 secured to the front end of handguard 14. The parts are locked in this position by a split pin 34 press-fitted into simultaneous engagement with the contiguous surfaces of both 7 gas cylinder 26 and barrel 12.

Gas cylinder 26 is formed with a central bore 36 the front end of which is blocked by a cylindrical plug 38 retained in place by a suitable press-fitted pin 49. Since the forward end of plug 38 extends beyond the front end of gas cylinder 26, a cover 42 mounted to the front end of plug 33 serves to block entry of dirt or other foreign material into cylinder 26. The rearward portion of plug 38 is formed with a plurality of sealing ring surfaces 44 to minimize the escape of gas from cylinder 26. Rearwardly of ring surfaces 44, plug 38 is reduced in diameter to form a projecting circular stud 46 for limiting the forward movement of a piston 48 designed to impart rearward movement to operating rod 16.

Piston 48 is a cylindrical member consisting of a forward head portion 50 mounted in gas cylinder bore 36 for slidable contact with the interior surface thereof and a trailing rod portion 51 of sufficient length to protrude rearwardly from cylinder 26 into abutment with the front end of operating rod .16 :when the recoiling parts are returned to battery position. The diameter of rod portion 51 is smaller than that of bore 36 to provide an annular clearance for the passage of discharge gases against the annular shoulder 52 formed by the larger diameter of head portion '50. Annular shoulder 52 is '3 m3 interrupted by a plurality of longitudinal grooves 54 equally spaced about the circumference of head portion 59 of piston 48. 30, gas cylinder bore 36 is first enlarged to form an annular pocket 56 and thereafter decreased in diameter, as indicated at 58, for close slidable contact with the exterior surface of gas piston 48. a

In automatic operation of the firearm, a portion of the discharge gases which accompany and follow the passage of a fired projectile 60 through the bore of barrel 12 enter into gas cylinder bore 36 through gas ports 23 and 30. As these gases move forwardly about the reduced diameter portion 51 of piston 43 and pass into grooves 54, the pressure against the interrupted wall surfaces of annular shoulder 52 serves to hold piston 48 in abutment with stud 46 on gas plug 38 as best shown in FIG. 1. However, as the gases enter intothe open area surrounding stud 46, the force imparted to the driving or front face of piston 48 will increase until it exceeds the force tending to hold gas piston 48 stationary. Thereupon, gas piston 48 will begin to move rearwardly and impart recoil movement to operating rod 16.

Since the concept of locating a gas port adjacent the rear end of a gas cylinder permits the discharge gases to be channeled forwardly in opposition to the recoil movement of the gas piston, such movement can be delayed until the required quantity of discharge gases is accumulated in the gas cylinder. Thus, in the event environmental conditions require an increase or decrease in power, this can be readily accomplished merely by replacing the existing gas piston with another having a more favorable ratio between the opposing surface areas against which the discharge gases are directed. In firearms with conventional gas cylinder structure in which the initial movement of the piston precludes further entry of gas into the cylinder, any desired change in power would require a corresponding change in the size of the gas port in the barrel. Obviously, if this were done, it would not be possible to again utilize the firearm under normal conditions.

Furthermore, the relatively smooth and gradual manner in which the gas piston of the present invention is accelerated minimizes the initial impact imparted to the operating rod. As a result, the unlocking of the breech and the subsequent movement of the recoiling parts is effected without the peak stresses and strains normally encountered in firearms in which the piston is actuated in direct response to the entry of the discharge gases into the gas cylinder.

Although a particular embodiment of the invention has been described in detail herein, it is evident that many variations may be devised within the spirit and scope thereof and the following claims are intended to include such variations.

I claim:

1. In a gas-operated firearm having a barrel and a reciprocal operating rod, a gas system comprising a cylinder Immediately to the rear .of gas port 5 secured to the barrel, a piston having a head portion slidably disposed in said cylinder and a trailing rod por- 7 tion. of reduced diameter projecting from said cylinder into abutment with the operating rod, closure means positioned in the front end of said cylinder to contact the front end of said piston head portion and form an annular area adjacent thereto for accumulating discharge gases therein, gas port means in said cylinder for admitting discharge gases from the barrel against the rear end of said piston head portion to initially retain said piston against rearward movement out of contact with said closure means, and a plurality of gas passages circumferentially spaced about said piston head portion to admit discharge gases into said accumulation area whereby recoilmovement of said piston is initiated as soon as the force on the front end of said piston head portion exceeds the force on the rear end thereof.

2. The combination defined in claim 1' wherein said closure means comprises a plug fixedly secured in said gas cylinder, a cap' secured to the front end of said plug for sealing the forward end of said gas cylinder, and a cylindrical stud of reduced diameter projecting centrally from the rear end of said plug for contact by the front end of said piston head portion.

3. In a firearm having a barrel, a gas cylinder fixedly secured to the underside of the barrel, a piston having a head portion in slida ble contact with the interior of said cylinder, a rod portion of reduced diameter projecting rear-wardly from said head portion to define an annular shoulder at the junction therebetween, closure means fixed in said cylinder to seal the forward end thereof, a cylindrical stud of lesser diameter than said closure means projecting rearwardly therefrom to contact the front end of said piston head portion and form an annular gas chamber adjacent thereto having a rear wall surface of greater area than the corresponding surface of said annular shoulder, a gas port located in the rear end of said cylinder, a gas port in the barrel in axial alignment with said gas port in said gas cylinder whereby the discharge gases are intially directed against said annular shoulder of said piston, anda plurality of longitudinal gas passages circumferentially spaced about said piston head portion in communication with said annular gas chamber adjacent the front end thereof whereby recoil movement of said piston is delayed until the force of the discharge. gases accumulated in said gas chamber adjacent the front end. 'of said piston head portion exceeds the force of the incoming discharge gases on said annular shoulder.

References Cited by the Examiner UNITED STATES PATENTS 960,825 6/10 Colleoni 89-191 2,918,847 12/59 .Barr n 89'1 91t BENJAMIN A. BORCHELT, Primary Examiner.

FRED C. MATTERN, JR., Examiner. 

1. IN A GAS-OPERATED FIREARM HAVING A BARREL AND A RECIPROCAL OPERATING ROD, A GAS SYSTEM COMPRISING A CYLINDER SECURED TO THE BARREL, A PISTON HAVING A HEAD PORTION SLIDABLY DISPOSED IN SAID CLYLINER AND A TRAILING ROD PORTION OF REDUCED DIAMETER PROJECTING FORM SAID CYLINDER INTO ABUTMENT WITH THE OPERATING ROD, CLOSURE MEANS POSITIONED IN THE FRONT END OF SAID CYLINDER TO CONTACT THE FRONT END OF SAID PISTON HEAD PORTION AND FORM AN ANNULAR AREA ADJACENT THERETO FOR ACCUMULATING DISCHARGE GASES THEREIN, GAS PORT MEANS IN SAID CYLINDER FOR ADMITTING DISCHARGE GASES FROM THE BARREL AGAINST THE REAR END OF SAID PISTON HEAD OF PORTION TO INITIALLY RETAIN SAID PISTON AGAINST REARWARD MOVEMENT OUT OF THE CONTACT WITH SAID CLOSURE MEANS, AND A PLURALITY OF GAS PASSAGES CIRCUMFERENTIALLY SPACED ABOUT SAID PISTON HEAD PORTION TO ADMIT DISCHARGE GASES INTO SAID ACCUMULATION AREA WHEREBY RECOIL MOVEMENT OF SAID PISTON IS INITIATED AS SOON AS THE FORCE ON THE FRONT END OF SAID PISTON HEAD PORTION EXCEEDS THE FORCE ON THE REAR AND THEREOF. 